BOOKS.
TIDAL LANDS.* IT is significant that an engineer and a botanist should have joined in writing this very able and interesting book on shore problems. Their collaboration emphasizes the important truth that science must mobilize all its forces if it is to solve the manifold difficulties of defending the coast and reclaiming land from the sea. The great contractor who builds massive sea-walls without counting the cost cannot afford to neglect the assistance of the geologist, or of the modest botanist who unobtrusively studies seaweed, or of the physicist who is concerned with wave-motion and the dynamics of pebbles and sand. Our coasts are strewn with the wrecks of ambitious schemes planned by engineers who were insufficiently ad- vised by men of science ; witness, for example, the works which were intended to improve the port of Chester, and have in fact caused the Dee to silt up. On the other hand, the theoretical study of sand-waves enabled the engineers of a Peruvian desert railway to devise a simple method of preventing the sand dunes from over- whelming the track. They strewed grit and pebbles on the rear flank of the dunes, thus interfering with the ripple action of the sand and causing the dunes to assume irregular shapes, which the wind attacked and scattered. It is a pretty illustration of the practical value of pure science, which is exemplified repeatedly in this book.
. Professor Oliver, who has long made a special study of shore plants at the University College station at Blakeney Point, Norfolk, brings out very clearly the reasons why plants are "pee-eminent as agents in the protection and growth of tidal and coast lands." Each typo of shore has its own vegetation, and man may do good deal to encourage the spread of the plants which are most capable of fixing an unstable shore of sand or shingle or mud. The problem of the sand dune was solved long ago in Holland and in the Landes south of Bordeaux. Two lines of brushwood fences are set in the sand above high-water mark. A dune rapidly forms between and above the fences, which attract all the drifting sand. Marram-grass (psamma) is then planted in this artificial dune, which attains its final shape by the end of the second year. The grass has the curious property of keeping pace with the accumu- lation of sand, pushing up buds to the new surface, and also extending horizontally, so that the whole dune is penetrated by its roots and tendrils. When the dune has become stable, rnarram.gra.ss ceases to flourish. It is then time to plant trees; the pines, alders, and birches do best. On Lord Leicester's estate at Holkham, on the Norfolk coast, three hundred acres of dunes have been planted with pines during the last half-century, converting a barren waste into a fine belt of woodland. South of Bordeaux the efforts of four generations have covered the dunes with great forests of maritime pine ; the export of pit-props to England alone from this region
• Tidal Lands a Study of Shore Problem. By Alfred E. Carey and F. W. Oliver. London: Mackie and Son. [12s. Od. aztj was said to reach six hundred thousand tone a year before the -war, so that the sand has, in Arthur Young's phrase, been turned into gold. It will surprise many people to learn that a shingle beach, unpromising as it looks, can be planted as readily as a sand dune.. The shingle on an open shore collects great quantities of organic matter and soil, and, strangely enough, its upper part is full of fresh water. The authors remark that during the severe drought of 1911 the shingle beaches in the South of England, espe- cially the Chesil Bank, were found to have as abundant a vege- tation as usual, though the mainland behind them was parched.
• The typical shingle plant is Suaeda fruticosa, the shrubby sea blite, a woody shrub growing to a height of three or four feet. This plant grows on beaches that are covered at the spring tides, but thrives also on sand dunes, or even in a London window-box. In mobile shingle it seems to flourish under rough treatment, pushing out new lateral shoots whenever it is covered by a fresh layer of pebbles, and thus gradually ascending the lee side of a bank and consolidating the shingle as it goes. The authors declare that Suctecla is un- rivalled in its power of growing in and holding shingle, and that a strip seven yards wide planted on the crest of a shingle beach will rapidly cover the surface layers with such a dense mat of vegetation that the beach will cease to move—obviously an important matter for bungalow settlements such as exist at Shoreham and elsewhere. As for the great stony wastes at Dungeness, which has ten thousand acres of shingle, or Rye, or Orford Ness, the authors "hare little doubt they could be converted into forest areas without great difficulty." There remain the salt-marshes—the " saltings " or
high marsh, which are covered only at spring tides, and the "slob lands," which are covered by every tide. The staple plant of the
salt-marsh is Salicornia, one variety of which is gathered as " sem- phire "on the East Coast. But a remarkable newcomer is Spartina Townsenclii, or "rice-grass," to which Lord Montagu of Beaulieu
drew attention in 1907. This grass, first reported in Southampton Water in 1870, has now covered thousands of acres of the mud-flats in that district. Within the last twenty years it has spread over large tracts of Poole Harbour. It anchors itself in soft mud by long roots and grows to a height of two or three feet. It grows in clumps which rapidly unite to form meadows ; the soft mud is
thus consolidated and becomes safe grazing-land. There seems, indeed, to be some reason to fear lest Spartina should reclaim too much tidal land in Poole Harbour and Southampton Water, so as to interfere with navigation. The economic properties of such a plant deserve study.
The authors have much to say about the maritime engineer's methods of coast defence, and about the traditional methods of re- claiming land either by "warping "—that is, allowing the silt- laden tides to flow over marshes until the level is raised—or by embanking. They declare that the problem of erosion is a vary serious one, and that it ought to be faced as a national and not as a local question. The Royal Commission that sat from 1906 to 1911 was informed by the Director of the Ordnance Survey that in thirty- three years the United Kingdom had made a net gain of 41,362 acres from the sea, whereas the Board of Agriculture declared that there had been a net loss of 182.000 acres :— "The notorious fact remains," say the authors, "that, whereas large areas of land are disappearing under attacks of the sea, corre- sponding areas of reclamations or innings are not in evidence. Whichever way the balance of area goes, it is obvious that the land which is being washed into the sea is for the most part good agricul- tural land, and in some cases valuable town land ; while the land from which the sea recedes is in the main a sandy swamp of little intrinsic value."
For lack of a uniform policy, the efforts of one district to protect its coast-line may be nullified by the neglect of the adjacent districts. The lamentable case of Hallsands, near Start Point, illustrates the failure of the State to realize its responsibilities. This fishing village was protected by a broad shingle beach with a sea-wall. In 1896 a firm of contractors was licensed by the Board of Trade to dredge gravel and sand opposite Hallsands, far use in the construction of the new Devonport Dockyard. The removal of the natural defences of the village led, six years later, to the collapse of the sea-wall, and in 1917 the whole village was destroyed in a north-easterly gale. The value of a wide beach or a shingle bank close to the shore was ignored in this case as in many others. The authors point out very justly that the Local Authorities who thrust promenades out below high-water mark deliberately make trouble for themselves, and that the wise policy for coast towns is to leave a broad strip of land between the beach and the houses, so that the highest tides may expend their fury in vain. The force of a storm is enormous, and only the most massive and costly embankments can resist the battering of masses of water driven forward by a gale. The authors cite one curious illustration of this in regard to the Chesil Bank, that remarkable natural bulwark of the Western Dorset coast. This bank of shingle is four hundred feet wide at high tide and about thirty-four feet above the Fleet, as the backwater behind it is called. Yet in heavy weather the waves break right over it, carrying shingle into the Fleet. After the sinking of the ' Formidable ' on New Year's Day, 1915, one of the boats drifted ashore on the Chesil Bank. Thirty
men tried in vain to haul it to the top. But a month later a heavy sea lifted the boat and flung it clear over the bank on to the lee slope. We seem to recall a similar story of a small naval vessel with her crew being carried over the Bank into the Fleet, on the crest of a huge wave ; in view of the well-attested experience of the Formidable's ' boat, the older story may well be true. Yet the stupendous energies of the sea can be controlled, if they are rightly understood, and the authors of this admirable book have thrown much new light on the whole engrossing problem.
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